A silicon-on-sapphire (SOS) integrated circuit includes a plurality of spaced, isolated islands of single-crystalline silicon on the surface of a sapphire substrate. Each island generally includes an MOS field-effect transistor which has source and drain regions spaced by a channel region, a channel oxide layer over at least the channel region and a conductive gate on the oxide layer and over the channel region. The various MOS field-effect transistors are electrically connected to form a desired circuit, such as a complementary MOS (CMOS) integrated circuit. The MOS field-effect transistors are generally electrically connected, at least in part, by conductive interconnects of polycrystalline silicon which extend over the surface of the sapphire substrate between the various silicon islands.
When such an SOS integrated circuit is used in an environment where it is subjected to radiation, the radiation creates secondary electrons as it passes through the sapphire substrate. These secondary electrons have a high kinetic energy, greater than 20 electron volts for sapphire, which is rapidly lost through scattering events until they are thermalized to the conduction band. These electrons then drift in an electric field, causing current flow, until they are either trapped, recombined with ionized core atoms, or pass through device contacts. Thus, in an SOS integrated circuit in which polycrystalline silicon conductors are directly on the surface of the sapphire substrate, the photogenerated electrons in the sapphire will flow into the polysilicon conductors which conduct the electrons into the field-effect transistors in the silicon islands. This flow of electrons can adversely affect the operation of the circuit formed in the SOS integrated circuit.